1. Field of the Invention
The present invention relates to a bus switch and an electronic switch.
2. Description of the Related Art
Conventionally, a bus switch is used for connecting and disconnecting a pair of buses, for example, provided in a local area network of a vehicle (i.e., in-vehicle LAN). In a system disclosed in U.S. Pat. No. 6,448,671, a master and one or more slaves are coupled in a daisy chain manner through a pair of buses for responding to a fault condition. The master and the one or more slaves are coupled in the daisy chain manner or are coupled in parallel, and electronic switches are coupled in series to one side of the pair of buses for connecting and disconnecting the daisy chain. In a system disclosed in U.S. Pat. No. 5,964,815, one side of a pair of buses can be connected and disconnected by switching an N-channel metal oxide semiconductor transistor (nMOS transistor) by using a control circuit.
In the above-described systems, when an abnormality of a bus potential (e.g., open or short) occurs, the abnormality is difficult to be avoided. Thus, if the bus is shorted to a power source or ground, a slave circuit may be adversely affected.
In a case where an nMOS transistor is used as a switch of the bus, if the bus is shorted to ground, a drain potential may decrease below a source potential. Thus, a parasitic element may generate and the switch is difficult to be disconnected. This sort of abnormality due to the parasitic element may occur not only in the bus switch but also in an electronic switch for switching energization and deenergization.